Propeller blade de-icing



April 17, 1956 F. M. LE COMPTE ET AL 2,742,248

PROPELLER BLADE DIE-ICING Filed Feb. 16, 1952 2 Sheets-Sheet l A ORNEY April 1955 F. M. LE COMPTE ET AL 2,742,248

PROPELLER BLADE DE-ICING Filed Feb. 16, 1952 2 Sheets-Sheet 2 A TO EY United States Patent PROPELLER BLADE DE-ICING Frank M. Le Compte, Moorestown, Don R. Woolf, Caldwell, and Edwin F. Mittenzwei, North Caldwell, N. 3., assignors to Curtiss-Wright Corporation, a corporation of Delaware Application February 16, 1952, Serial No. 275,634

8 Claims. (Cl. 244-134) This invention relates to de-icing of the blades of aircraft propellers and provides particularly, improvements in the electrical de-icing of hollow steel propeller blades wherein the electrical heating element is disposed inside of the blade.

One of the most practical and effective ways to prevent icing of the propeller blades or to remove ice after ice has formed is to heat the blades electrically, and various methods and arrangements have been used and have been suggested for this purpose. Poekel Patent No. 2,402,770 issued June 25, 1946, shows an internal electrical heater for hollow steel propeller blades wherein a woven resistance wire pad is bonded within the propeller blade. Sheets Patent No. 2,638,295, issued May 12, 1953, shows the use of external electrical resistance shoes on propeller blades and also, means for conducting electricity to the shoes and for cycling the electrical power intermittently to the shoes. Enos Patent No. 2,619,305, issued November 25, 1952, shows an arrangement for de-icing wherein a metallic tube is brazed within the leading edge of a hollow propeller blade, the'tube being adapted for the conduction of the de-icing medium which may be fluid such as alcohol. j Y

i In the present invention, the teachings of the three above mentioned inventions are, in a sense combined in an inventive manner so that internal electrical heaters may beinstalled in propeller blades for maximum heating efiectiveness, and for improvement on the structural characteristics of the propeller blade. The invention involves the use of an electrical heater which has been proved in service to be exceptionally rugged and effective. In addition, the heating arrangement of the present invention may be applied to existing hollow steel propeller blades with comparative ease and without affecting the heat-treatment of the propeller blade to any significant degree The invention is shown in the annexed drawings-in a preferred embodiment, but the scope of the invention is not limited by the specific embodiment shown and described hereinafter except as limitations may be imposed by the claims forming a part of this specification.

In the drawings, Fig. 1 is a plan of a propeller blade, partly in section, to show the characteristics of the invention, Fig. 2 is a cross section substantially in the mid-span of the propeller blade incorporating the invention, Fig. 3'is an enlarged elevation, partly in section, showing the heater component, Fig. 4 is a sectional elevation of an electrical connector adapted to conduct electrical power to the heater, and Fig. 5 is a section through a blade showing an alternative form of the invention.

' A hollow steel propeller blade is shown at 6 in Figs. 1 and 2, and it comprises a shank portion 7 adapted to be secured in a propeller hub in a manner well known in the art. The blade comprises thrust and camber plates 8 and 9 respectively terminating at their edges in a thickened trailing edge 10 and a thickened'leading edge portion 12. Withinthe leading edge portion is disposed 2,742,248 Patented Apr. 17, 1956 unit is formed from a known electrical resistance heater construction known as calrod, the heater being in rod form but comprising an external metallic tube 16 con-v taining a concentric layer 17 of refractory insulating material, the insulation 17 embracing an electrically conductive resistance wire 18, which may be a straight filament or a helically coiled filament. This type of heater unit is exceptionally stable, may be operated at very high temperatures without failure, has excellent resistance against the effects of vibration, and may be constructed for any desired power consumption and heating effect within reason.

As used in this invention, the rod heater is formed of a single rod including a connector portion 29, an inner limb portion 22, a loop end 24, a rear limb portion 26, and a final connector portion 28. When formed as shown in Fig. 3, the rod limbs 22 and 26 are brazed or soldered together as at 27 to constitute an integrated heater unit. A gusset plate 3i) is formed to fit the opening in the loop 24, the edges of the plate 30 being brazed or soldered as at 31 to the heater rod forming the loop to reinforce the loop and to minimize failure thereof as a result of possible vibrative stress. The rod ends 20 and 28 are secured to an elongated cup 32 which is secured to the edges of an opening 34 formed in the shank portion of the propeller blade. The ends of the resistance Wires within the rod heater protrude into the cup as at 36 and 37 for engagement by an electrical connector shown in Figs. 1 and 4. If desired, the heater rod ends may be carried on through the blade hollow and connections thereto may be made within the propeller hub.

After the heater rod unit shown in Fig. 3 is fabricated as a sub-assembly, it is bent as necessary to conform to the contour of the inside of the blade leading edge 12 and is set within the blade with the cup engaging the blade-opening 34. lacking devices may be used at several points along the rod heater to hold the heater in contacting relation with the blade material. Thereupon, wire spelter or solder of appropriate length and composition is inserted along the heateras at 33 with appropriate fiux, and the blade is heated adjacent the leading edge to fuse the solder or brazing material whereby a filleted fused metal bond is established between the heater unit and the leading edge of the propeller blade as at 35. The

cup 32 may also be bonded byfused metal to the shank a heater unit 14 shown, enlarged, in Fig. 3. The heater portion of the blade through which it passes.

The preferred solder for securing the heater within the blade is an alloy of cadmium and silver whose flow temperature is in the neighborhood of 725 F. This alloy has an exceptionally high tensile and shear strength and yet flows at asufficiently low temperature so that the heat treatment of the steel of the propeller blade is not affected in any way. This enables detachment and attachment of a heater unit in a finished propeller blade. There are other solders and brazing materials which may be used in securing the heater in the blade, some of these being high strength, high temperature materials such as silver solder which can be utilized during manufacturing processes of the propeller blade and will Withstand heat treatment to which the blade is subject during manufacturing processes and operation. However, when such solders or brazing materials are used, replacement'of heating elements within the blade requires re-heat treatment of the blade before it is suitable for operational use.

For the reasons indicated above, the low temperature hard solders are desirable; low temperature soft solers are likely to have insufiicient strength to meet the operas ing stresses to which the blade is subject. The connector plug of Fig. 4 comprises connecto sleeves-59 and 49 contained within a shell-'32, the counectors being molded in insulating material 44. Conarcane-s ductors 45 and 46 lead from the connectors to contact strips 47 and 48 which are secured to slip rings, 49 and 50 embracing the blade shank '7 in insulated relation. The housing for the strips 47 and 43, shown at 52 .in the construction for the slip rings and connector strips, may be substantially the same as that shown in Sheets Patent No. 2,638,295 and mentioned above.

it will be appreciated that the heater 14 and the cup 32 form a part of the final blade assembly. When the blade is installed in a propeller, the slip rings 49 and h are assembled, the connectors 39 and '20 are engaged with the prongs 36 and 37, and the shell 42 is secured to the cup 32 by means of a through bolt 54. Connections are established between 4?: and 5t whereby electrical power is made available to the heater 4.

The present invention has advantages over the electrical heating arrangement of the prior art in that the internal heater transmits heat to the leading edge portion of the blade by direct conduction through the fused metal bond, leaving the external hard surface of the blade intact, without protuberances which interfere with the air foil section of the blade, or which interfere with the inherently high abrasion resistance of the propeller blade. The heater 14 may be installed and removed without great ditiiculty and when installed, is as good as the propeller blade from a structural standpoint.

In this invention, it will be noted that two terminals for the electrical heater are brought out in insulated relation to the propeller blade so that a pair of electrical contacts are provided. In some prior art. systems, the blade itself or the tube forming part of the heater has been used as a ground for an electrical return. The present arrangement is superior to those utilized in a ground return as firm electrical contacts are assured. In a grounded return system, high resistance points may creep into the system which lessen the efiectiveness of the heater.

The provisions of the invention are applicable to solid blades as well as to hollow steel blades. Rod heaters may, for instance, be inserted in grooves formed in or near the leading edge of solid metallic blades, and secured to the blade by fused metal which is used in sufiicient quantity to fill the blade groove and form a part of the blade surface. Fig. 5 shows such an arrangement, wherein 56 is the blade, 58 a groove therein, 60 the rod heater and 62 the fused metal.

Though but a single embodiment illustrating the invention has been shown and described, it is to be understood that the invention may be applied in other and various forms. Changes may be made in the arrangement, without departure from the spirit of the invention. Reference should be had to the appended claims for definitions of the limits of the invention.

What is claimed is:

1. In a unitary hollow propeller blade, an electrical heater unit'comprising a metallic tube including a limb extending along and within the propeller blade adjacent the blade leading edge, from the blade shank toward the tip, said tube being looped at a point within the blade and extending from the loop toward the shank as a second limb lying adjacent the first limb and superimposed on the first limb, said two limbs being secured to one another and to the blade structure by filleted fused metal, said tube containing a concentric layer of refractory insulating material and an electrically resistive conductor, said tube loop within the blade including a gusset plate filling said loop and secured to the tube at the loop by fused metal.

2. In a unitary hollow propeller blade, an electrical heater unit comprising a metallic tube including a limb extending along and within the propeller blade adjacent the blade leading edge, from the blade shank toward the tip, said tube being looped at a point within the blade and extending from the loop toward the shank as a second. limb lying adjacent the first limb and superimposed another and to the blade structure by filleted fused metal,

said tube containing a concentric layer of refractory insulating material and an electrically resistive conductor, said fused metal which secures the heater unit in the blade having a flow temperature of the order of 700 F.

3. In a unitary hollow propeller blade, an electrical heater unit comprising a metallic tube including a limb extending along and within the propeller blade adjacent the blade leading edge, from the blade shank toward the tip, said tube being looped at a point within the blade and extending from the loop toward the shank as a second limb lying adjacent the first limb and superimposed on the first limb, said two limbs being secured to one another and to the blade structure by filleted fused metal, said tube containing a concentric layer of refractory insulating material and an electrically resistive conductor, said blade being of steel, and said fused metal which secures the heater unit in the blade having a flow temperature substantially less than the lower critical temperature of the steel. v

4. In a unitary hollow steel propeller blade, an electrical heater including a metallic substantially circular sheath having a first limb extending within and in contact with the leading edge of the blade, said sheath being looped at its outer end and having a second limb extending along the first limb and in contact therewith, fused metal bonding said sheath limbs to one another and to the blade steel and forming fillets with the sheath and blade steel, providing a strengthening fillet for the blade and providing a solid metal heat flow path from the heater through the sheath and fillet material to the blade steel, said fillet metal having a How temperature substantially less than the lower critical temperature of the blade steel.

5. In a unitary hollow steel propeller blade, an electrical heater including a metallic substantially circular sheath having a first limb extending within and in contact with the leading edge of the blade, said sheath being looped at its outer end and having a'second limb extending along the first limb and in contact therewith, fused metal bondingsaid sheath limbs to one another and to the blade steel and forming fillets with the sheath and blade'steel, providing a strengthening fillet for the blade and providing a solid metal heat flow path from the heater through the sheath and fillet material to the blade steel, said fillet metal having a flow temperature substantially less than the lower critical temperature of the blade steel and comprising a silver-cadmium alloy.

6. In a unitary hollow steel propeller blade, an electrical heater including a metallic substantially circular sheath having a first limb extending within and in contactwith the leading edge of the blade, said, sheath being looped at its outer end and having a second limb extending along the first limb and in contact therewith, fused metal bonding said sheath limbs to one another and to the blade steel and forming fillets with the sheath and blade steel, providing a strengthening fillet for the blade and providing a solid metal heat flow path from the heater through the sheath and fillet material to the blade steel, and a gusset secured by fused metal to the sheath at the loop therein.

7. In a hollow steel propeller blade comprising steel plate portions integrally united to form a leading edge and a trailing edge and defining the blade hollow therebetween, an electrical heater comprising a tubular metallic sheath containing an electrical heating element in electrically insulated relation to the sheath, part of saidsheath extending along and within said blade adjacent the. leading edge thereof, from near the blade root toward the blade tip, said sheath toward the blade tip being doubled back on itself in a loop and having another part lying 7 adjacent the first part and extending from said loop tometal of low melting point compared with the melting points of the blade steel and the heater, securing said heater within and to the propeller blade for mechanical support of the heater in the blade and for conduction of heat from the heater to the blade material adjacent its 5 leading edge.

8. A propeller blade according to claim 7, including a metallic gusset of thin sheet metal having an outline like the inside of said loop, inserted in said loop and bonded to the heater sheath parts forming said loop.

References Cited in the file of this patent UNITED STATES PATENTS 1,784,528 Lidke et a1. Dec. 9, 1930 16 6 Waters May 26, 1931 Benson Feb. 23, 1932 Poekel June 25, 1946 Greenwald Jan. 21, 1947 Hardy Oct. 14, 1947 Hunter Nov. 30, 1948 Van Daam May 8, 1951 Young Apr. 8, 1952 FOREIGN PATENTS Switzerland Nov. 1, 1944 Great Britain May 27, 1943 Great Britain Jan. 29, 1947 

